Even if --dry-run mode was specified, the control file was getting
updated, preventing follow-up runs of pg_rewind to work properly on the
target data folder.  The origin of the problem came from the refactoring
done by ce6afc68.

Author: Alexey Kondratov
Discussion: https://postgr.es/m/7ca88204-3e0b-2f4c-c8af-acadc4b266e5@postgrespro.ru
Backpatch-through: 12